An international evaluation of the cancer preventive potential of vitamin A

The IARC convened a Working Group of experts in May 1998 to evaluate the cancer preventive potential of vitamin A and to compile the third volume of the IARC Handbooks of Cancer Prevention. The handbook is intended to provide a comprehensive review of the relevant information in the published scientific literature through April 1998 on the role of vitamin A in cancer prevention. The focus of this critical review and commentary is on retinol and the retinyl esters. Much of the scientific literature in this field overlaps with studies involving vitamin A metabolites, vitamin A precursors, and studies of total dietary vitamin A (which is a combination of preformed vitamin A and its precursors), so work from this wide range of research is included in this review when it is deemed relevant to our understanding of the effects of retinol or retinyl esters on cancer development. The observed effects of preformed vitamin A on cell and organ culture, on animal models, in dietary observational epidemiological studies, and in human intervention studies was reviewed in the meeting. In summary, there is little evidence that vitamin A intake has any substantial cancer-preventive effects.